I. Field of the Invention
The present invention relates generally to microturbine power generating systems, and more particularly to managing a battery source associated with a microturbine power generating system.
II. Description of Related Art
The use of distributed generators for the production of electrical power has been increasing steadily over the last decade. In many parts of the world lacking an electric infrastructure (e.g., transmission and distribution lines), the commercialization of distributed generators has been greatly expedited since central plants will not only cost more per kilowatt, but will also need expensive infrastructure installed to deliver power to consumers of electricity. In the United States and other countries already having the electric infrastructure, the small, multi-fuel, modular distributed microturbine generation units will allow consumers of electricity to choose the correct method of electric service. The small, multi-fuel, modular distributed microturbine generation units will also allow consumers of electricity to choose the most cost-effective electric service.
Small, multi-fuel, modular distributed microturbine generation units could help alleviate current afternoon xe2x80x9cbrownoutsxe2x80x9d and xe2x80x9cblackoutsxe2x80x9d that are prevalent in many parts of the world. For examples of microturbine power generating systems, see U.S. Pat. Nos. 4,754,607, 6,064,122 and 6,147,414, all of which are assigned to the assignee of the present invention. These microturbine power generating systems includes a turbine engine, a compressor and an electrical generator, with each device including a rotating component (e.g., a turbine wheel, a compressor wheel and a permanent magnet rotor).
Microturbine power generating systems such as the ones described in the ""122 and ""414 patents include an external battery source. The battery source is used at start up to power the electrical generator that turns the compressor until the turbine engine is capable if sustaining combustion. The ""122 further discloses that the battery source can supply backup output power if the electrical generator experiences a failure. The charge on the battery source is typically maintained by charging the battery source with a portion of the output power when the microturbine generating system is operating. In order to maintain a sufficient charge, the turbine generating system may have run as often as several times a month, or more often in cold environments, which may be costly in terms of fuel consumption.
In addition, microturbine power generating systems have finite power limits defined by numerous factors such as the design of the turbine engine and the inverter. Thus, when a system is in normal operation and a large inductive load is added, the system may take several seconds to accelerate the turbine engine to a point that the demands of the additional load are met. While the impact of such a transient load can be reduced by using a microturbine power generating system with a higher power limit, this is often not a viable solution because systems with higher power limits usually cost more.
Thus, there exists a unsatisfied need in the industry for improved means for charging the battery source of a microturbine power generating system and for minimizing the impact of a transient load on the output of a microturbine power generating system.
The present invention provides systems and methods for managing a battery source associated with a microturbine power generating system, including charging the battery source from the utility grid when the turbine engine is not running and providing load support when the microturbine engine is unable to support the full load. The present invention may includes a battery charging circuit for controlling the charging of a battery source from the utility grid, a voltage boosting circuit for controlling the provisioning of load support and a controller for controlling the operation of the charging circuit and the voltage boosting circuit.
The battery charging circuit derives power to charge the battery source from either a utility grid connection or from the electric generator output. The charging source power is conditioned through an alternating current (ac) transformer and rectifier. The direct current (dc) output of the rectifier is supplied to a down chopper that provides a constant current to the battery source. The level of current is determined from sensors that measure battery temperature and voltage and is controlled by the controller. The characteristics of the battery and the temperature are used by the controller to set the charging current level and the maximum charging voltage. The same ac source can also be used to supply a thermostatically controlled heater for batteries that may be exposed to extremely low temperatures.
The voltage boosting circuit regulates the voltage of the battery source that is provided to a dc converter. The regulated output voltage can be used to either supply energy to start a microturbine engine or alternatively provide energy to support load demands when microturbine is not able. The controller uses a voltage regulator and current limiter to protect the battery and a battery voltage detector to prevent excessive discharge of the battery.